1. Field of the Invention
The present invention relates to a color-information processing method for performing pseudo-three-dimensional display in order to analyze a color distribution.
2. Description of the Related Art
Recently, with the widespread use of personal computers and work stations, desktop publishing (DTP) and CAD (computer aided design) have been widely used. In such a situation, a color reproducing technique of colors represented on a monitor using color materials becomes important. In DTP, for example, in a computer system including a color monitor and a color printer, formation, editing, processing of a color image are performed on a monitor, and the obtained color image is output from the color printer. The user strongly desires that the color image on the monitor perceptually matches with the output image from the printer.
In the color reproducing technique, however, it is difficult to achieve perceptual matching between the color image on the monitor and the output image from the printer because of the following reasons.
That is, in the color monitor, a color image is represented by emitting light of a specific wavelength using a phosphor for each color pixel. On the other hand, in the color printer, a color image is represented by absorbing light of a specific wavelength using ink or the like and utilizing remaining reflected light for each color pixel. Due to such a difference in the image display mode, the color reproduction range greatly differs between the two types of color images. Even in color monitors, the color reproduction range differs among a liquid-crystal monitor, a CRT (cathode-ray tube) using electron guns, and a plasma display. Likewise, in color printers, the color reproduction range depends on the quality of paper, the amount of use of ink, and so on. Therefore, to achieve the perceptual matching among color images in display media having different color reproduction ranges, various gamut mapping techniques exist.
Although the quality of these various gamut mapping techniques is determined ultimately by subjective evaluation for various input images, it is costly and also difficult to reflect the result of the evaluation upon the gamut mapping technique. Accordingly, an analysis/evaluation method for a gamut mapping technique is needed, in which the result of the analysis/evaluation can be reflected on the gamut mapping technique.
As conventional analyzing techniques for determining the quality of a gamut mapping technique, calculation of the sum of color differences for all colors, evaluation of a color difference for each color, and the like are used.
However, because an image is obtained by combining color information and spatial information, quality of gamut mapping technique must be evaluated by taking into consideration whether or not spatial information is well preserved when image is color-converted by gamut mapping. Whether preserving spatial information is well or ill preserved depends on whether or not gradation is well preserved by a gamut mapping. However, since the above-described quantitative evaluation method does not take gradation information into account, only one side of the gamut mapping technique can be evaluated.
In addition, since color information is distributed in a three-dimensional space, the amount of quantitative-evaluation information is large, hence it is difficult to obtain the desired local information.